1. Field of the Invention
This invention relates to DC to AC inverters and to voltage controlled oscillators.
2. Description of the Prior Art
Modern switching power supplies that use bipolar junction transistors require a source of power to drive the base circuit of the power switch. The following characteristics are generally required: a power range of one to ten watts; transformer isolation; and variable frequency. Most prior devices use a saturable reactor to control frequency. However, varying of the output frequency can only be accomplished by changing the input voltage to the device. Additionally the range of control is severely limited because the output power is also modulated. Although a variety of integrated and discrete circuit techniques are currently utilized as the control element for the base circuit drive, these circuits tend to be extremely complex because they not only require a drive transformer and discrete transistors, but also need additional circuits to control frequency.
One such device is described in U.S. Pat. No. 3,217,171 to P. D. Corey for a "Variable Frequency Oscillator." This reference combines a magnetic coupled multivibrator and a saturable reactor wherein the control winding of the saturable reactor is connected to a DC control signal which varies the frequency of the multivibrator as a function of the amplitude of the DC control signal. However, this reference does not include the magnetic amplifier nor the novel feedback means of the present invention by which the flux excursions in the output transformer are balanced to prevent saturation.
U.S. Pat. No. 3,223,945 to W. E. Damon describes a "Controllable Frequency Magnetically Coupled Multivibrator." This rather complex implementation is directed towards circumventing the perceived requirement for a low impedance control source for the multivibrator. In any event, the construction of the reference device is significantly different in almost all respects from that of the present invention.